The possibility of dialogue between the United States and North Korea is being cautiously raised even after the U.N. Security Council's (UNSC) adoption of harsher-than-ever sanctions against Pyongyang.

One instance backing the possibility was unofficial talks held in Switzerland between a former high-ranking U.S. government diplomat and a senior North Korean foreign ministry official.

Japan's NHK reported Thursday that Evans Revere, former U.S. principal deputy assistant secretary of state for East Asia, exchanged views with Choe Kang-il, deputy director general of the North Korean foreign ministry's North American affairs bureau, while the two were attending a three-day international security conference on Northeast Asia that wrapped up Wednesday.

What they discussed during their talks remained unknown as Choi refused to answer reporters' questions and left the venue by car, NHK added.

But it is believed that among the issues was the latest sanctions resolution unanimously approved Monday by the UNSC on the Kim Jong-un regime in response to its sixth nuclear test conducted Sept. 3.

It is viewed that the new sanctions resolution was harsher than ever, but also left some room for dialogue as its final version was significantly watered down compared to the draft circulated by the U.S. last week.

The final version eliminated a total ban on oil supplies to the impoverished state and an international asset freeze on North Korean leader Kim Jong-un and his sister, Yo-jong ― measures included in the draft resolution.

Observers say Washington may have taken a step back from the maximum level of sanctions bearing in mind the possibility for dialogue with Pyongyang.

The U.S. State Department stressed Wednesday that Washington will not give up using diplomacy to persuade the North to give up its nuclear and ballistic missile programs.

"Diplomacy, we will not give up on," Heather Nauert, the department spokeswoman, said during a briefing with foreign reporters. "That is still first and foremost, that is the preferred approach."

Nauert said her department is "realistic" but also "optimistic" that diplomacy will resolve the issue, adding that if this effort fails, the Treasury Department can use unilateral sanctions and the Department of Defense has a "portfolio of things they can certainly do."

Last month, it was belatedly known that the United States and North Korea had been communicating behind the scenes for several months.

At the time, The Associated Press said, "Diplomatic contacts are occurring regularly between Joseph Yun, the U.S. envoy for North Korea policy, and Pak Song-il, a senior North Korean diplomat at the country's U.N. mission."

Earlier this month, Foreign Minister Kang Kyung-wha told a National Assembly Session that the ministry shared the need for playing a role in pulling off the Pyongyang-Washington conversation.

"The ministry will play such a role when there are conditions for it to take place," she said.

For their part, military authorities are paying keen attention on the possibility for the regime in Pyongyang to carry out additional military provocations to protest the new sanctions.

They said the North could choose the founding anniversary of the ruling Workers' Party, which falls Oct. 10, to conduct such a provocation.